Conventionally, research has been directed toward a technology that involves forming a pn junction, via a diffusion layer, on a surface of a small-diameter spherical semiconductor element made of a p-type or n-type semiconductor and then connecting a plurality of these spherical semiconductor elements in parallel to a common electrode, this technology being put to practical use for solar cells, semiconductor photocatalysts, and so forth.
U.S. Pat. No. 3,998,659 discloses an example in which a solar cell is constituted by forming a p-type diffusion layer on the surface of a n-type spherical semiconductor, connecting the respective diffusion layers of a plurality of spherical semiconductors to a common film-like electrode (positive electrode), and then connecting the n-type core sections of these spherical semiconductors to a common film-like electrode (negative electrode).
U.S. Pat. No. 4,021,323 discloses a solar energy converter (semiconductor module) having the following constitution. Plural p-type spherical semiconductor elements and plural n-type spherical semiconductor elements are placed in series, and connected to a common film-like electrode, and respective diffusion layers of these semiconductor elements are made into contact with a common electrolytic solution, and then by irradiating with solar light, electrolysis of the electrolytic solution is induced.
So too in the case of the modules having spherical cells appearing in U.S. Pat. Nos. 4,582,588 and 5,469,020, because the spherical cells are attached by being connected to a sheet-like common electrode, a plurality of spherical cells are suitable for connecting in parallel. However, they are not suitable for serial connection.
On the other hand, as shown in International Patent Publication Nos. WO98/15983 and WO99/10935, the inventor of the present invention has proposed a granular light emitting or light receiving semiconductor device in which a diffusion layer, pn junction, and a pair of electrodes are formed on a spherical semiconductor element made of a p-type semiconductor or an n-type semiconductor. Also, proposed is a semiconductor module, which is produced by connecting a plurality of the semiconductor device in series and then connecting a plurality of the serially connected bodies in parallel, and which can be applied to a solar cell, a photocatalyst device for electrolysis of water and so forth, a variety of light emitting devices, and color displays, and the like.
In the case of this semiconductor module, when any semiconductor device of any serially connected body enters an open state due to failure, current no longer flows to the serial circuit including above failed semiconductor element, and the remaining normal semiconductor devices in the serially connected body also enter a breakdown state, whereby dropping of the output of the semiconductor module is generated.
In addition, in the case of the spherical semiconductor devices having the positive and negative electrodes that were proposed by the present inventor, handling is a problem because the device is prone to rolling, and it is not easy to determine the position for forming the positive and negative electrodes nor to distinguish the positive and negative electrodes during assembly.
Therefore, the inventor of this application undertook research with respect to a technology for forming a pair of flat surfaces on a spherical semiconductor element and then for forming electrodes on these flat surfaces. However, not only was there then a large number of processes for the electrode formation, it also became evident that it was still not easy to distinguish between the positive and negative electrodes and that this technology was not very advantageous in terms of mass producing the semiconductor module by using a multiplicity of spherical semiconductor devices.
An object of the present invention is accordingly to provide a substantially spherical semiconductor device having one flat surface, is not prone to rolling and can be handled easily. Another object of the present invention is to provide a semiconductor device in which a first electrode is formed on the flat surface and a second electrode is formed at the apex on the opposite side to this electrode such that the center of the semiconductor device is interposed between the first and second electrodes, and in which the positive and negative electrodes can be easily distinguished. A further object of the present invention is to provide a making method for this semiconductor device.